I guess you'll have to make another batch!I was reading this thread and I planned to backsweeten my coffee wine with brown but I did with white one. Damn, I totally forgot. I started it in January and bottled in late March. I didn't open even one bottle. I'm not sure how long coffee wine should be aged.
I think some brown sugar adds a nice touch. I've also added a little to banana, ginger, and some pear wines with nice results. Personally I like about 25% brown sugar.